The invention relates to a rotor blade arrangement of the type utilizing fiber composite material.
Worldwide efforts are being made to reduce the engine weight in the construction of turbine aero engines by using fiber composites (FVW). Modern engines, particularly for commercial airplanes, have a high bypass ratio and therefore considerable dimensions of the fan blades or prop-fan blades. These blades, which rotate at very high rotational speeds, are subject to high stress caused by centrifugal force and must therefore be manufactured of high-strength materials.
Because of their high tensile strength in combination with their low specific weight, the use of fiber composites is suggested for blades of this type. However, in this case, the introduction of forces, particularly of the centrifugal forces and of the stresses caused by foreign-object impact, from the fiber-structured blade to the metallic hub has been solved only insufficiently. In constructions known in prior art, the fiber-structured rotor blade is glued or riveted onto the metal base constructed as a blade core.
Since the shearing strength and the crushing strength of fiber composites is considerably lower than that of metals, it has not been possible to construct the blade base of fiber composites, whereby a functionally effective transfer of force from the blade to the hub would have to be ensured. For this reason, the blade is constructed of metal. However, in this case, there is the problem of a good introduction of force, because the connection is mainly constructed to be frictional and not form-locking.
A rotor blade of this type is known from German Published Unexamined Patent Application (DE-OS) No. 20 42 665, in which the fiber strands wind around an axially arranged pin and are hung into a slot of the metallic blade base. It is a disadvantage that the fibers are stressed by pressure in a relatively small section in order to absorb the centrifugal forces.
From German Published Unexamined Patent Application (DE-OS) No. 16 28 286, a blade fastening system is known for an axial fan, in which the fiber strands wind around a pin, the pin being arranged in a connecting piece. In this case, the blade can be pivoted laterally and has low bending resistance.
An object of invention is therefore to achieve a good introduction of the forces occurring during the operation from the fiber-structured blade to the metallic blade base, in which case the fiber materials are to be stressed only with respect to tension.
According to the invention, this object is achieved by providing an arrangement including:
Blade core means provided with a plurality of core webs spaced from one another and extending radially toward a rotor rotational axis when in an in use position on a rotor,
fiber loops made of fiber strands wound onto the blade core means to form a blade with a portion of said fiber loops extending between said core webs to anchor said fiber loops at the blade core means,
and blade core anchoring means for anchoring said blade core means to a rotor by way of said core webs and separately of the fiber loops, whereby said fiber strands are securely anchored to said rotor while being stressed only in tension in response to centrifugal forces acting on the blade during rotational operation of the rotor
A most important advantage of the invention is that the fiber strands of the blade are hung in at the supporting core and as a result during the operation are stressed only with respect to tension. Consequently, the high tensile strength of the fibers can be utilized advantageously. In this case, the blade is fastened at the rotor by means of a number of webs distributed over the central section of the supporting core, the guide blade being fastened at the rotor side by means of these webs.
As a result of the arrangement according to the invention, a good transfer is possible of the centrifugal forces occurring during the operation to the rotor, without any unfavorable stress to the fibers of the guide blade--for example, with respect to pressure. In addition, a very stiff suspension of the guide blade is achieved which, at the same time, results in a low weight.
In certain preferred embodiments the supporting core has the shape of a wedge with a lobar rounded head in its cross-section, permitting a good winding-around by the fiber strands.
In certain preferred embodiments it is advantageously provided that the webs have uniform distances from one another. This results in a good load distribution.
According to a preferred further development of preferred embodiments of the invention, the webs are connected with a round blade base plate, which, by means of a ring-shaped collar, is fastened on the rotor side. As a result, a good adaptation can be achieved of the fastening device to a swivel mechanism for the blades integrated in the rotor. In this case, the connection of the webs and the blade base plate advantageously takes place by means of welding, particularly electronic beam welding. The latter has the advantage of a low heat development, whereby a previously mounted fiber material will not be damaged.
As an alternative, it is contemplated to manufacture the supporting core and the blade base plate as one piece, and to insert the fiber strands, in the central section of the supporting core, through the openings between the webs. The fiber strands in the web area, in this case, must be glued on subsequently.
In an alternative embodiment of the invention, the webs are constructed in their cross-section to be dovetailed. They are preferably surrounded by a metallic casing, whereby a dovetailed ,construction of the blade base is achieved, similar to the constructions known from compressor or turbine blades. This permits a blade fastening which requires little space and which avoids the risk of a blade failure as a result of material defects in the fastening device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.